Our group has continued studies of chromatin structure and the regulation of heat shock gene expression, with emphasis on the structure and function of the heat shock transcription factor (HSF) and on the remodeling of the heat shock gene promoter in chromatin. Yeast two- hybrid screens have been conducted to identify interacting proteins for Drosophila HSF. Biophysical studies of HSF oligomerization have determined the equilibrium dissociation constants for the monomer-trimer transition, the first step of HSF activation by heat shock. These studies show that temperature does not affect HSF trimerization directly, but through other pathways, which are currently being explored. Our group has also continued work on the ATP-dependent nucleosome remodeling factor (NURF) discovered in this laboratory. The flexible histone tails, especially those of histone H3 and H4 were found to be involved in stimulating the ATPase activity of NURF. Three out of four subunits of NURF have been identified and are currently being characterized. Using highly purified NURF, the Laboratory showed that NURF is capable of facilitating transcriptional activation on a reconstituted nucleosomal template. This demonstration shows for the first time that the direct action of a nuclesome remodeling factor is crucial for activating gene transcription under conditions that closely mimic those inside the cell, and provides clear and substantial support for the significance of this new family of transcriptional facilitators generally termed "chromatin remodelers" in regulating genetic activity in health and disease.